The objective of this paper is to determine the incidence and severity of the FAW (Spodoptera frugiperda J.E Smith) and to study the influence of the cropping system on the degree of infestation of FAW in the cultivated corn fields in Kivira locality. To achieve these objectives, 60 corn fields including 20 fields at the 4 leaf stage, 20 fields at the 8 leaf stage and 20 fields at the flowering stage were visited. At the end of the analysis, the results show that the number of diseased plants was significantly higher for the 8 leaf stage with an average of 7.44 plants compared to the other two stages of corn development. Likewise, in corn fields at the 8 leaf stage, the number of FAW larvae in an area of ​​25 m2 is much higher with an average of 9.79 larvae. As with the number of diseased plants and larvae, the study shows that the number of lesions per leaf at the 8-leaf stage is greater than the number of lesions per leaf at the other phenological stages. The incidence of Fall Armyworm varies significantly with the phenological stages and crop types associated with corn. The average incidence of FAW in fields at the 8 leaf stage is higher than in other phenological stages. The averages are 35.72%, 9.88% and 6.96% for the 8 leaf stage, the flowering stage and the 4 leaf stage respectively. The average severity index for the Fall Armyworm is 7.24%. The maximum value obtained is 22.53%. At the 8-leaf stage, the average severity of FAW is 17.57% compared to 2.32% for the flowering stage and 1.83% for the 4-leaf stage.